This invention relates to the field of paper sizing compositions, and particularly to an improved unfortified rosin based paper size which comprises a stable, homogeneous mobile liquid that is fully miscible with water.
Although useful as paper sizing materials, various rosins, including tall oil rosin, are relatively insoluble in water.
In order to improve their properties, rosins to be used in paper sizing are typically modified by condensation with an aldehyde, or fortified by relation with .alpha., .beta. unsaturated dibasic acid or anhydride such as fumaric acid, maleic acid or maleic anhydride. In accordance with currently prevailing practice, rosin sizes are usually fortified rosins. In the preparation of paper from unbleached pulp, it has generally been found that the unfortified rosins are preferred over fortified rosins.
While fortified rosin sizes are available in a number of forms, including paste, liquid, dry, and water dispersed, unfortified rosin sizes are typically available only in paste form. Such paste typically contains about 70% solids. However, to render it miscible with water and therefore useful in the sizing of paper, rosin paste must be heated to elevated temperature, typically in the range of 70.degree.-80.degree. C. or higher. Even at such temperatures, the degree of miscibility with water is somewhat limited. Hot compositions produced from rosin paste normally contain only up to about 12-14% by weight solids. This hot liquid composition is further diluted to 3-5% solids at ambient conditions, before being mixed with the pulp suspension. The relatively low water miscibility of unfortified rosin paste makes it expensive or impractical to convert it to liquid form for shipment, storage or handling. Accordingly, the paper maker must provide facilities for melting the paste and maintaining it in a molten form prior to use.
This melting and mixing process requires equipment and energy. It would be an advancement in the art to provide an unfortified rosin in liquid form, to facilitate handling in the paper mill, particularly in those unbleached pulp applications in which unfortified rosin size is preferred.
Emerson et al U.S. Pat. No. 4,022,634 describes a liquid sizing composition comprising an aqueous mixture of ammonia, an ammonium salt, and a fortified rosin. The fortified rosin is saponified with a base and mixed with the reaction product of urea and an acid such as sulfamic acid, phosphoric acid, oxalic acid, methanesulfonic acid, trichloracetic acid, nitric acid, sulfuric acid, hydrochloric acid, stearic acid, or acetic acid. In producing the fortified rosin, tall oil rosin is reacted with from 9-30% of an organic acidic compound.
Emerson et al U.S. Pat. No. 4,025,354 also describes an aqueous sizing composition comprising rosin and the reaction product of urea and sulfamic acid. The disclosure is further directed to sizing compositions comprising hydrocarbon resin, stearic acid, wax, or mixtures of these components with each other or with rosin.
Emerson et al U.S. Pat. No. 4,437,894 describes a paper sizing composition comprising a fortified and saponified rosin mixed with the ammonium salt of formic or sulfamic acid. The ammonium salt may be produced, for example, by the reaction of urea and formic acid.
Rummelsburg U.S. Pat. No. 2,720,514 is a relatively early patent describing treatment of tall oil rosin with an aldehyde in the presence of a strong acid catalyst to form a rosin/aldehyde condensation product. This reference is not specifically concerned with paper size.
Watkins U.S. Pat. No. 2,941,919 describes a paste size which comprises the reaction product of tall oil rosin and formaldehyde. The formaldehyde modification is said to improve sizing efficiency. The amount of formaldehyde reacted is 1-4% based on the weight of the tall oil rosin. The paste product is saponified.
Japanese Pat. No. 31[1956]-1604 describes a process in which rosin and urea are separately added to a pulp suspension to provide sizing to the paper produced from the pulp. According to the disclosure, the urea may be added at any stage of the rosin sizing process. Both the saponified rosin and urea are preferably added to the beater, i.e., the tank in which the pulp is sized and refined.
Japanese Pat. No. 48[1973]-48703 describes a sizing composition in which fortified and saponified rosin is compounded with a urea/formaldehyde resin. The purpose of the urea formaldehyde resin is to promote the solubility of the potassium soap of the rosin.
Japanese Pat. No. 46[1971]-18283 describes the preparation of a rosin-type sizing agent which is said to be effective in hard water. The sizing agent is produced by reacting fortified rosin with urea, partially saponifying the reaction product with a nitrogenous base, such as ammonia, an amine, or an alkanolamine, and further saponifying with an alkali metal base such as potassium hydroxide, sodium hydroxide, potassium carbonate, or sodium carbonate. A water miscible organic solvent such as methanol is added to the resulting composition.